1. Field of the Invention
This invention relates generally to a composition and method for testing smoke detectors of both the ionization and photoelectric type and, more particularly, to a composition and method for dispensing the composition by an aerosol spray can for testing smoke detectors of both types.
2. Brief Description of the Prior Art
There are two basic types of smoke detectors. One is an ionization detector which senses changes in the conductivity of the air in a measuring chamber or chambers under the influence of radioactive radiation. The other is a photoelectric detector which senses the scattering of light in a measuring chamber.
In an ionization type of detector, an electric field is set up between two electrodes by a DC voltage. When the air between the electrodes is ionized by the radioactive source, the resulting ions move under the effect of a field in the direction of the oppositely charged electrodes. Electric current results in a manner whereby the current strength depends on the number and velocity of the ions. When fire aerosols penetrate into the space between the two electrodes, a part of the ions is deposited onto the particles of these aerosols which are substantially heavier than the ions. The heavy ions move less freely as a result of the increase in mass inertia and thereby no longer contribute to the carrying of the charges thereby diminishing the current. The detector, in turn, senses the diminished current and sounds an alarm.
In the smoke detectors of the photoelectric type, there is provided a semiconductor diode which provides an infrared light source, the silicon cell operates as a light receiver, and a light absorber provides protection from light from sources outside the chamber. The diode emits light through pulses in the shape of a hollow cone; and, as long as the measuring chamber does not contain any smoke, the infrared light does not reach the receiver placed in the center axis of the light cone. When smoke penetrates the measuring chamber, smoke particles disperse the light rays in all directions and a part of the dispersed light reaches the photoelectric receiver which then produces an electric signal sounding the alarm.
As is well known, such smoke detectors are widely used as safety devices which are designed to protect lives and to reduce property damage by providing a warning of fire when the fire is in its earliest stage. How fast the smoke detector responds is of particular importance, since the time interval between the warning alarm and the spread of the fire through the building is a critical factor. A few minutes is often the difference between survival and death.
Detectors may fail to sound an alarm as quickly as required because their sensitivities can become altered over a period of time by dust, grease, corrosive fumes, moisture or by other contaminants in the area in which the detector is located. Electronic component failures are also known to occur as a result of aging, etc. Detector manufacturers typically provide for testing the device by means of pressing a test button or by pulling a switch which is located in the housing of the unit. Alternatively, some models can only be tested by blowing smoke in the direction of the detector through smoke derived from a cigarette, cigar, match, candle, paper, rope, etc.
There are major disadvantages in the conventional testing of smoke detectors. Since the recommended placement of smoke detectors is on the ceiling or high up on the wall, a person of average height must stand on a chair or on some elevation in order to press the button, pull the switch or blow the smoke, thus risking physical harm which could be a serious matter for older people. At best, blowing smoke is a clumsy and primitive method for testing such devices. Testing by way of a button or switch only assures that the alarm is operative and provides no indication as to whether the sensing chamber is operative.
One solution to this problem has been suggested in U.S. Pat. No. 4,301,674, entitled "Smoke Detector Tester", by W. Haines et al., issued Nov. 24, 1981, which shows a smoke detector tester comprising a handheld aerosol container for holding under pressure a quantity of spray emitted from the container by a finger valve in the form of an aerosol cloud within the sensing area of the smoke detector undergoing test. The contents of the aerosol spray can contain a hydrocarbon propellant, isopropyl alcohol and dioctyl phthalate which provides the particles in the aerosol detected by the smoke detector. The particles on the aerosol are provided by the dioctyl phthalate which can leave an oily residue. Other compositions that can be dispersed from aerosol cans for testing smoke detectors are suggested in U.S. Pat. No. 4,715,985, entitled "Composition for Checking the Functioning of Fire Detection Installations and Application to Various Types of Detectors", issued Dec. 29, 1987. The primary component suggested for these compositions is trichlorotrifluoroethane which may cause adverse environmental problems.
Therefore, it is a primary object of this invention to provide a composition for testing smoke detectors primarily by dispersion from an aerosol can in a manner that is economical, nontoxic and environmentally safe without leaving an oily residue.